Cell polarity or asymmetry is fundamental to the development and morphogenesis of all organisms. Over the past two decades, the subcellular localization of RNAs that encode transcription and translational regulators of gene activity has emerged as a major mechanism underlying cellular asymmetries. Our molecular understanding of how the initial asymmetry plays out in terms of regulating gene activities and cell identities within an embryo has grown rapidly. By comparison, the cellular mechanisms that underlie the cytoplasmic transport and localization of mRNAs are not well understood. We are studying the asymmetric transport of mRNA determinants required for the specification and differentiation of the Drosophila oocyte. The Drosophila oocyte exhibits some of the best studied examples of the mRNA localization strategy. Most notably, the localization of Bicoid mRNA to the anterior and Oskar mRNA to the posterior of the oocyte is critical for establishing axial patterning in the embryo. Genetic analysis has described a pathway of gene products that act in a stepwise fashion to restrict the localization of Bicoid and Oskar mRNAs. This pathway most likely includes specific components that act in trans to regulate the recognition, transport, and targeting of specific RNAs. Other components of transport may not be specific to oogenesis and are yet to be identified. Our plan includes three specific aims. 1) We will characterize the in vivo motility of GFP-tagged components of the anterior/posterior (A/P) pathway. The motors responsible for transport will be determined using strategies to disrupt or eliminate motor function. 2) Biochemical studies will be pursued to investigate the composition of the RNP complexes in an effort to identify the molecular link(s) to motor proteins. 3) To characterize new gene products identified in a novel screen that exhibit microtubule-dependent accumulation in the oocyte. The function of two newly identified loci as potential components of the RNP transport machinery in oocyte development will be investigated.